Hybrid vertical drainpipe heat exchanger

ABSTRACT

A low-cost hybrid heat exchanger uses sheet copper and rigid plastic tubing. Copper is used only where actual heat transfer takes place, adjacent the drainpipe wall. All other components are plastic to lower cost. It pre-heats fresh cold water using waste heat from the drain such as from a shower drain. The heat exchanger comprises an inner copper conduit or drainpipe, a rolled sheet copper cylinder, an outer plastic tube and manifolds, and O-ring. On assembly, inserting the drainpipe results in the O-ring being compressed between the copper cylinder and the plastic tube. The result is a sealed water chamber wherein heat transfer takes place. The ends of the plastic tube have radially spaced water distribution holes into the chamber and inlet and outlet manifolds, each with water connections to the building&#39;s cold water supply. A method of recovering heat from non-shower hot water uses using a separate reservoir is also disclosed.

FIELD OF THE INVENTION

The present invention is in the field of heat exchangers and moreparticularly drainpipe heat exchangers for drainwater heat recovery fromvertical drainpipes.

BACKGROUND OF THE INVENTION

Drainwater is a low-level heat source. As such it requires a low costheat exchanger in order that home and building owners can recover itscost in a reasonable time.

SUMMARY OF THE INVENTION

While it may be used in a variety of heat transfer applications, instantheat exchanger's use in heat recovery from a building's wastewaterdrainpipe will be described in detail herein. The instant heat exchangeris suitable for both vertical and horizontal installations. Wheninstalled vertically it operates as a falling film heat exchanger wherethe drainwater flows circumferentially on the inner wall which maximizesthe wetter surface area needed for heat transfer. Typically, verticalinstallations are limited in length by ceiling-to-floor dimensions inbuildings which, in turn, limits the wetted surface area.

By moving the relative locations of its plumbing fittings, it can beused horizontally, where it is preferably made as long as possible tomaximize wetted surface area for heat transfer which directly affectsperformance and cost-effectiveness.

The heat exchanger comprises a set of concentric cylindrical components.At the center is a conduit such as a standard drainpipe made of copperor other thermally conductive material.

Around it is a shorter cylinder of sheet copper (or other thermallyconductive material). This cylinder is open along its length to define asmall gap. Concentric with the cylinder and spaced from it (i.e., oflarger diameter) is a outer tube of plastic or other rigid, low-costmaterial, which has a ring of spaced holes that are covered by amanifold at each end.

Next is a unique gasket-spacer, such as a common O-ring, that followsthe perimeter of the copper cylinder and thereby defines the boundary ofa sealed chamber one wall of which is the cylinder and the other theplastic tube. The inner openings of the ring of holes are also enclosedby the gasket.

The short cylindrical plastic manifolds are sealed to the outside of theplastic tube and have has an internal circumferential groove and a waterfitting. The fitting opens into the groove within which the outeropenings of the ring of hole are located.

Thus water (or other fluid) for heat transfer with the centraldrainpipe, enters the sealed chamber at one end and exits at theopposite end of the outer tube.

Heat transfer takes place in the chamber, either heating or cooling,depending on the relative temperatures of the drainwater and the freshwater. For most uses heating of the freshwater will be the goal.However, for example, a drinking fountain can use the instant inventionto cool the delivered water using draining cold water to cool freshincoming warmer water.

The diametric dimensions of the components ensures that upon finalassembly of the components, the first described drainpipe, which isinserted last, is a press fit into the cylinder which causes the O-ringto compress sealing the chamber.

Inside the chamber, the building's normal water pressure exerts enormousforce on the cylinder close the gap slightly to create an extremelytight clamping action around the drainpipe for maximum thermalconductivity. For example with water pressure of 50 psi and a cylinderarea of 200 square inches, the circumferential clamping force onto thedrainpipe is 10,000 pounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of the heat exchanger also showing the waterflow through the fittings, manifolds and chamber;

FIG. 2 is an exploded view of the outer tube and the manifolds;

FIG. 3 shows how the O-ring is shaped with its hoop ends and straightruns when installed adjacent the inner wall of the outer tube, and thetwo opposing O-ring rods located on the opposite wall of the outer tube;

FIG. 4 shows the central drainpipe and surrounding cylinder with itslongitudinal gap;

FIG. 5 shows the relationship between the drainpipe, cylinder and O-ringand a representation of how the pins work to hold the O-ring. The pinsactually protrude through the wall of the outer tube;

FIG. 6 shows the concentric layout of the components without themanifolds and showing how pins protrude through the outer tube to engagethe O-ring until it is secured in place on final assembly;

FIG. 7 shows how the cylinder could be made from a trapezoidal sheet toprovide an angled gap;

FIG. 8 is schematic drawing of how the instant heat exchanger having athird centre manifold can be used to recover heat during batch water usesituations where used hot water is draining from say, a dishwasher, butno cold water if flowing to the faucet or water heater. The separatereservoir will automatically thermosiphon its water supply through theheat exchanger thereby recovering heat from the drainpipe.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 shows a cross section of the drainpipeheat exchanger 100. The central drainpipe 14 may be a common copper DWV(domestic waste vent) tube or pipe of any suitable diameter from, say, 2to 6 inches. It may also be rolled and seamed from any suitable sheetmaterial. In FIGS. 1 and 2 outer tube 1 may be of any suitable stillmaterial such as a PVC or ABS plastic tube or pipe capable ofwithstanding pressure from within and sized in accordance with thediameter of drainpipe 14. Outer tube 1 has fluid openings adjacent eachend preferably in the form of a ring of holes 9 through the wall forfluid distribution.

Inlet manifold 4 (lower) and outlet manifold 4 a (upper) have inlet 5and outlet 6 fittings (inlet flow 15 a, outlet flow 15 b) and aninternal circumferential flow channels 10 that communicate with theirrespective distribution holes 9 in outer tube 1. As shown in FIG. 2 themanifolds arrows indicate they are to be slid on over each end of outertube 1. The distribution holes may be spaced and/or sized so as tooptimize heat transfer performance. That is, more or bigger holes arebetter the further away they are from the fittings, 5, 6.

The manifolds 4 and 4 a are orientated such that the inlet 5 and outlet6 are positioned opposite to where the gasket O-ring gap 3 c will belocated on assembly. For horizontal operation, a third centralizedmanifold 4 b may be added for the inlet 5 and the two end manifolds 4, 4a used collectively as outlet 6.

The manifolds can be fabricated from four parts: a short section ofplastic tube with two spaced plastic rings 11 inside, and a plastic pipefitting, all bonded together and defining a circumferential flow channel10. Alternatively flow channel 10 may be formed internally by machiningan internal groove in a piece of thick wall tube or pipe. The manifoldsare bonded to secure and seal them to outer tube 1. The manifolds mayalso be fitted with O-rings (not shown) that seal against the outer wallof outer tube 1. Of course the flow channel 10 may be formed in theouter circumference of outer tube 1 instead of, or, in addition to, itsindicated location inside the manifolds 4, 4 a (not shown). A pluralityof flow channels may be formed using a plurality of elements extendingbetween the O-rings.

A third manifold 4 b (dashed outline) of the same design may also beadded around the middle of the outer tube inclosing a ring ofdistribution holes (not shown) and with a water fitting. Using manifold4 b as the water inlet the water flow therefrom is both up and down (orleft and right if horizontal, with gasket gap 3 d downwards). In thisway a remote water tank or reservoir can be plumbed inline with theinstant heat exchanger to enable thermosiphonic flow therebetween forheat exchange with batch water flow.

Inlet manifold 4 may have a fluid pressure regulator fitted (not shown)to limit the internal pressure in chamber 15.

Cylinder 2 may be least expensively formed from sheet copper whichremains open (un-seamed) along its length. Preferably it has at leastone longitudinal flange 2 a shown in FIGS. 4 and 6 that serves to indexcylinder 2 in the O-ring gap 3 d (FIG. 3) and prevent its unwantedrotation during assembly. Gap 7 enables cylinder 2 to clamp tightly ontodrainpipe 14, first during assembly by means of the compression ofO-ring 3, 3 a, 3 b, 3 c, and then when installed, as a result of theenormous force created by the internal water pressure. Gap 7 also servesthe important function of providing a vent or fluid path to the ambientin the event of a leak developing in the heat exchanger between thedrainpipe 14 and cylinder 2 whereby a visible drip will signal a servicerequirement.

FIG. 1 shows how a open plastic hoop 20 (dashed outline) can beimplemented to prevent erosion of the cylinder 2 from the jets of waterthat would otherwise impinge directly on the cylinder surface slowlyeroding it.

FIG. 3 shows the gasket-spacer component which operates in a marginalarea around the perimeter of cylinder 2. An O-ring may be used. It isslightly stretched to hook over pins 16 (FIGS. 2, 5, 6) to create theend hoops 3 a separated by the straights 3. Pins 16 are preferablyinserted through the wall of outer tube 1 where one end protrudes intochamber 15 and the other end terminates in flow channel 10. Alternatelypins 16 may be attached to cylinder 2. Opposite the O-ring straights 3are two rear compensators 3 c of similar gasket material that act ascompression elements to ensure even compression of straights 3 along thelength on either side of gap 7 of cylinder 2.

Once assembled the O-ring elements maintain a sealed spacing betweencylinder 2 and outer tube 1 which defines a chamber 15 (FIG. 1) throughwhich water flows for heat transfer therewith. Chamber 15 may haveinserts to provide turbulent flow, such as plastic mesh, rings, beadsand the like. Further this chamber 15 may be made to hold more or lesswater by altering the O-ring diameter including using large bore tubingor by adding a shaped spacer under the O-ring and bonded to the interiorwall of the outer tube. In this way a reservoir is formed to hold aquantity of water. This would be advantageous in applications such asbelow a sink where a supply of hot water is undesirable due to plumbingor operational costs, as, for example, in a restaurant. With enoughvolume the instant heat exchanger can provide warm water at no cost andmaintain a warm flow by using the draining used water to heat theincoming cold water.

Cylinder 2 may be fabricated with an angled gap 7 a as shown in FIG. 7which will avoid an unbalanced inwards force that would exist along theotherwise axial gap 7 where no water pressure is exerted.

FIG. 6 shows how the components are arranged concentrically, how pins 16engage O-ring 3,3 a, how flange 2 a engages the O-ring gap 3 d, and howthe O-ring is compressed between cylinder 2 and outer tube 1 definingchamber 15 (FIG. 1) and sealing same.

In FIG. 8 is shown how the instant heat exchanger 100 may be plumbed toinclude a separate reservoir 110 which is in turn, is plumbed to a waterheater 120 (or a faucet, not shown) which supplies hot water via hotwater branch 108. Mains water pipe 106 enters a building and splits intotwo branches: cold water branch 101 and hot water heater supply branch102. All drainwater leaves via sewer connection 107. Hot water heatersupply branch 102 enters the center manifold of heat exchanger 100 andflows both up and down (dashed arrows) to exit via the two endmanifolds. The end manifolds are plumbed into reservoir 110 at its top103 and bottom 104. Due to the physical property of fluids includingwater, hotter water is lighter or less dense that colder water.Therefore water in reservoir 110 naturally stratifies with the coldestbeing at the bottom which is continuous with water contained in heatexchanger 100. Any heat in drainpipe 14 will heat water in chamber 15making it lighter. By natural convection it will therefore be displacedupwards by the heavier, colder water entering below. This thermosiphonicprocess continues automatically as long as the water in the chamber 15is warmer than the water at the bottom of reservoir 110, the end resultbeing that the water in reservoir 110 becomes warmer from the top down.Reservoir 110 is plumbed to hot water heater 120 which will thereforereceive that warmed water when the next demand for hot water causes coldwater from mains 106 to push all the warmed water in heat exchanger 100and reservoir 110 into water heater 120 and finally into hot waterbranch 108 and out the opened faucet (not shown).

Note that with this arrangement lower branch 104 can see two way flow atdifferent times (double-ended arrows): if there is cold water flowingthrough branch 102, flow through branch 104 (and branch 103) is to theleft into reservoir 110; if only used hot water is draining, then theflow in branch 104 will be to the right into heat exchanger 100 becauseof the above described thermosiphonic phenomena.

Although the invention has been shown and described with respect todetailed embodiments thereof, it should be understood by those skilledin the art that various changes in form and detail thereof may be madewithout departing from the spirit and the scope of the claimedinvention.

I claim:
 1. A vertical drainpipe heat exchanger for transferring heatfrom a drainpipe, said drainpipe heat exchanger comprising: a conductivelayer surrounding said drainpipe; a gasket spacer, said gasket spacerhaving channels to permit flow of fluid therethrough adjacent saidconductive layer; and an outer cylinder surrounding said gasket spacer,an inlet and an outlet within said outer cylinder to permit fluid accessto said channels.
 2. The vertical drainpipe heat exchanger of claim 1wherein said conductive layer has a vertically extending openingtherein.
 3. The vertical drainpipe heat exchanger of claim 1 whereinsaid gasket spacer comprises an upper ring, a lower ring, and aplurality of legs extending therebetween.
 4. The vertical drainpipe heatexchanger of claim 2 wherein said outer cylinder has a plurality ofinlets and a plurality of outlets to permit fluid access to saidchannels.
 5. The vertical drainpipe heat exchanger of claim 3 whereinsaid conductive layer has a vertically extending opening therein, saidconductive layer having a flange adjacent said opening, said legs ofsaid gasket spacer being located adjacent said flange and said opening.